This invention relates to paraffin scrapers for oil wells and particularly to a novel type of paraffin scraper consisting of one or more molded plastic paraffin scraper blades, molded in place around a sucker rod and the mode of securely fastening the same to a sucker rod.
An oil well generally comprises a casing, a string of smaller steel pipe inside the casing and generally known as the tubing, a pump at the bottom of the well, and a string of steel rods, commonly referred to as sucker rods, within the tubing and extending down into the pump for operating the pump. Various devices as are well known in the art are provided at the top of the well for reciprocating the sucker rod to operate the pump.
In many cases, the means for reciprocating the sucker rods include devices for rotating the rods through a predetermined angle during each stroke of the sucker rods. Suitable apparatus of this character are shown by Sargent in U.S. Pat. No. 1,653,510; Poulson in U.S. Pat. No. 2,180,880; and McConahey et al. in U.S. Pat. No. 2,444,842; as well as by Johnston in U.S. Pat. Nos. 2,280,408 and 2,318,315.
The crude oil generally contains paraffin and other substances which tend to congeal and precipitate out of the oil and deposit upon the walls of the tubing during the passage of the oil through the tubing. Such deposits are quite objectionable and tend to restrict the flow of oil through the tubing. Various means and methods have been proposed for preventing the formation of such deposits and for removing deposits so formed. Such means and methods comprise the use of chemicals, electrical heating and various mechanical scraping devices. In general, such means and methods are expensive and have other objectionable features.
A common mode of preventing the formation of deposits on the tubing and removing such deposits as they are formed, comprises attaching mechanical paraffin scrapers to the sucker rod. Such sucker rods remove the deposits from the oil well tubing as it is formed so that it is flushed out of the well with the oil passing therethrough.
During and from the beginning of the post-World War II period, significant developments were made in the attachment of scrapers to sucker rods.
C. E. Blackburn in U.S. Pat. No. 2,321,275 disclosed a simple solution for the then-existing problem in the form of an inexpensive detachable scraping blade for sucker rods which are simultaneously reciprocated and rotated. While such scraper blades of Blackburn were commercially successful, it ultimately became apparent that it was difficult to fasten the blade to the sucker rod sufficiently firmly and there was consequently a tendency for the blade to become loose in operations extending over long periods of time.
R. C. Lister in U.S. Pat. No. 2,468,503 disclosed an improved method for attaching scraper blades of the type disclosed by Blackburn to the sucker rod. While the method of Lister was also commercially successful, it required special welding operations in order to attach and secure the blades to the rod.
A further improvement to scraper blades of this type was developed by the inventor of this application, F. L. Carson, and is disclosed in U.S. Pat. No. 2,631,674.
Subsequent improvements were disclosed by Winegar in U.S. Pat. No. 2,979,133 and by Dunham in U.S. Pat. No. 3,106,962. Other notable developments in this technology include Donaldson's disclosure in U.S. Pat. No. 2,237,863 and Besse's disclosure in U.S. Pat. No. 3,156,286.
Paralleling these developments in metal bladed scrapers as early as 1937, attempts were made to develop related sucker rod guides, guards, stabilizers and scrapers from rubber or plastic materials. As disclosed by Anderson in his U.S. Pat. No. 2,153,787, these attempts often resulted in the rubber softening and swelling with the consequent result that the rubber member slipped on the rod and ultimately required replacement. Anderson proposed a solution in the form of a gamma polyvinyl chloride with a soluble plasticizer which upon extraction from the polyvinyl chloride resulted in its gripping the rod more firmly. Notwithstanding this development, a completely satisfactory solution in the form of rubber or plastic scrapers has never found substantial commercial success insofar as known by the applicants.
The multitude of reasons which may be responsible for the failure of such devices to obtain commercial success is no doubt only partially known to the applicants. However, as early as 1961, the applicant and his co-workers within assignee company undertook the development of various rubber and plastic scrapers including compositions formed from Buna N, polyurethane, poly-propylene, acrylonitrile and phenolic blends. In addition to material examination, various bonding means, adhesives, clamping devices, shrink fittings and other more sophisticated techniques were studied in detail. In general, it was found impossible to achieve the desired wear and service characteristics and/or to effectively and economically attach such scrapers to the sucker rod. As a result of these consistent failures, efforts to produce a rubber or plastic scraper were largely abandoned and lay dormant for a number of years prior to the present invention.
The attempts and efforts of others to find a suitable solution to the desire and need for a plastic or rubber scraper are detailed in the following U.S. Pat. Nos.: 2,402,223; 2,436,994; 2,572,307; 2,651,199; 2,693,986; 2,725,621; 2,810,143; 3,079,998; 3,186,773; 3,251,418; 3,414,337; 3,484,141; 3,528,499; 3,537,519; 3,560,060; and 3,537,519.
In addition to the various approaches noted above, a large number of patents have issued to J. C. Tripplehorn on plastic slotted spiral scrapers which are variously snapped on to a sucker rod. For example, see U.S. Pat. Nos. 2,928,472; 2,928,473; 2,969,115; 2,997,106; 2,870,845; 3,058,524; 3,083,772; 3,282,344; and 3,282,345.
A somewhat more recent development involves scrapers of a ball or dumbbell configuration for cleaning short radius of curvature sections. These also have generally been formed from plastic, rubber, or other resilient materials.
While many of the above patents have no doubt found specific application, none has provided the combination of elements to lead to its general utilization.
Insofar as it is possible to generalize, the prior art has failed to provide a scraper having wear characteristics superior to the characteristics possessed by the post-World War II metallic scrapers and the desired reliability and security of attachment to the sucker rod to prevent the paraffin scraper from becoming a significant part of the problem in the course of prolonged service as opposed to the desired solution to the paraffin problem.